Source : Webster's Revised Unabridged Dictionary (1913)

Rectilineal \Rec`ti*lin"e*al\ (-l?n"?*al), Rectilinear
\Rec`ti*lin"e*ar\ (-l?n"?*?r), a. [Recti- + lineal, linear.]
   Straight; consisting of a straight line or lines; bounded by
   straight lines; as, a rectineal angle; a rectilinear figure
   or course. -- {Rec`ti*lin"e*al*ly}, adv. --
   {Rec`ti*lin"e*ar*ly}, adv.

Source : WordNet®

rectilinear
     adj : characterized by a straight line or lines; "rectilinear
           patterns in wallpaper"; "the rectilinear propagation of
           light" [syn: {rectilineal}]